Lee went on a tirade against the president after screening 'BlacKkKlansman' at Cannes.

On Monday, Spike Lee wowed audiences at Cannes with a first look at BlacKkKlansman, his new film telling the riveting true story of a black cop who infiltrates the Ku Klux Klan in the 70s. But what really made waves at the screening was the impromptu speech Lee gave afterward—calling Donald Trump a "motherfucker" in a searing indictment of the alt-right, white nationalism, and intolerance, Vulture reports.

BlacKkKlansman, produced by Jordan Peele, is slated to hit theaters on the one year anniversary of the Charlottesville protests that led to the death of activist Heather Heyer. Lee ends his film with footage of the deadly car attack that took her life, a montage that reportedly left the Cannes audience in tears. When a theatergoer asked about the scene, Vulture reports, Lee went off on an anti-Trump tirade—denouncing the president's response to Charlottesville in a five-minute speech that left the director "shaken."

"We have a guy in the White House—I’m not gonna say his fucking name—who defined that moment not just for Americans but the world, and that motherfucker was given the chance to say we are about love, not hate," Lee said. "And that motherfucker did not denounce the motherfucking Klan, the alt-right, and those Nazi motherfuckers. It was a defining moment, and he could have said to the world, not just the United States, that we were better than that."

Lee slammed Trump's comments about the "violence on many sides" in Charlottesville, going on to make clear that his speech—and, ultimately, BlacKkKlansman itself—is a call to action.

"We have to wake up. We can’t be silent. It’s not a black, white, or brown [problem], it’s everybody," Lee said. "So this film, to me, is a wake-up call… stuff is happening, and it’s topsy-turvy, and the fake has been trumpeted as the truth. That’s what this film is about. I know my heart, I don’t care what the critics say or anybody else, but we are on the right side of history with this film."

According to the Hollywood Reporter, even before Lee gave his speech, BlacKkKlansman earned a ten-minute standing ovation at Cannes—a sign that the new film really is as good as it looks.